API 5CT N80-1 Seamless Casing Steel Pipe

API 5CT N80-1 is a "medium-to-high strength" grade within the oil casing hierarchy. The defining characteristic of N80-1 is its Normalizing heat treatment.

Process Detail: The steel pipe is heated to a temperature above the critical point (Ac3) by 30-50°C, held for a specific duration, and then cooled naturally in still air.

Microstructure: Through normalizing, N80-1 achieves a uniform and fine-grained Pearlite + Ferrite structure. This makes its mechanical properties significantly more stable than untreated J55/K55 and effectively eliminates residual manufacturing stresses.

Engineering Significance: This process ensures the pipe can withstand high collapse and tensile loads at depths of 2,000 to 4,000 meters.

Download Full N80-1 Technical Datasheets & MTCs-Ensure your project compliance with one click.

API 5CT N80-1 casing pipes Specification

Standard: API Spec 5CT (latest edition).

Steel Grade: N80-1.

Manufacturing Type: Seamless (S) or Electric Welded (EW).

Delivery Condition: Usually Normalized (N) or Normalized & Tempered (N&T). It can be Quenched & Tempered (Q&T) if agreed upon by the purchaser.

Thread Types: SC (Short Round Thread), LC (Long Round Thread), BC (Buttress Thread), and Premium Connections.

API 5CT N80-1 Casing Color Code

Color bands are used for rapid identification in the field:

N80-1: One Red Band.

API 5CT N80-1 oilfield casing pipe Chemical Composition

API 5CT focuses more on mechanical performance for N80, but places strict limits on Phosphorus and Sulfur:

API 5CT N80-1 Oil Casing Pipe Mechanical Properties

Mechanical requirements are the primary criteria for N80-1:

API 5CT N80-1 Casing Size Chart (Common)

The following are frequently used sizes for casing:

API 5CT N80-1 Casing Tolerance

Dimensions must adhere to strict API tolerances:

Outside Diameter (OD) Tolerance:

For D < 4-1/2": ±0.79mm

For D ≥ 4-1/2": -0.75% D to +1.00% D

Wall Thickness Tolerance: -12.5% (No upper limit for wall thickness, but restricted by weight tolerance).

Weight Tolerance: -3.5% to +6.5% for individual lengths.

Straightness: Maximum deviation shall not exceed 0.2% of the total length.

Inspection Methods and Standards

N80-1 seamless pipes must pass three primary stages of inspection before dispatch:

Hydrostatic Test:

Data Reference: Pressure is usually set at 80% of the SMYS (Specified Minimum Yield Strength). For a 9-5/8" 40lb N80 casing, the test pressure can reach approximately 3,950 psi (27.2 MPa), held for at least 5 seconds.

Non-Destructive Testing (NDT):

Ultrasonic Testing (UT) or Magnetic Particle Inspection (MPI) is mandatory to detect internal or surface defects such as cracks, folds, or laminations.

Drift Test:

A standard drift mandrel (typically 12 inches long for 9-5/8" casing) is passed through the pipe. If it doesn't pass under its own weight, the pipe is rejected.

N80-1 vs. N80-Q

Confused between N80-1 and N80-Q? Contact our engineers for a free selection guide and performance comparison.

Application Scenarios

API 5CT N80-1 Seamless Casing is a cost-effective, high-performance choice for modern oilfields.

When to choose it? Use N80-1 when the tensile strength of J55/K55 is insufficient to support the string's own weight, or the collapse strength is inadequate for formation pressures at ~3,000 meters, provided the environment is non-sour (no H2S).

Design Note: N80-1 is not a "sour service" grade. If H2S is present, you must upgrade to L80-1 or C90 to prevent sulfide stress cracking.

GNEE API 5CT N80-1 OCTG Casing Pipe process line

GNEE API 5CT N80-1 Casing Pipe test equipments

GNEE API 5CT N80-1 oilfield casing pipe certificate

FAQ

Can N80-1 casing be used in sour service wells?

API 5CT N80-1 casing is NOT recommended for sour service (H₂S environments).

Here is why:

Sulfide Stress Cracking (SSC): N80-1 is a high-strength steel that does not have controlled hardness or a specific microstructure to resist the brittle cracking caused by Hydrogen Sulfide (H₂S).

Heat Treatment: N80-1 is typically "Normalized," which leaves internal stresses that make it vulnerable to sour gas.

The Alternative: If your well contains H₂S, you should use API 5CT L80-1 or C90. These grades have the same strength as N80 but are specially treated (Quenched & Tempered) and hardness-controlled to survive sour service.

What connections are available for N80-1 casing?

N80-1 casing is available with two main types of connections:

1. Standard API Connections (Most Common)

STC (Short Round Thread): Used for shorter strings where tension load is low.

LTC (Long Round Thread): Provides higher tension strength and better sealing than STC.

BTC (Buttress Thread): Designed for heavy loads and high-tension applications; the most popular choice for N80 casing.

2. Premium Connections (Gas-Tight)

For high-pressure wells or wells requiring specialized sealing, Premium Connections (such as VAM, TenarisHydril, or Hunting types) can be applied to N80-1 casing to ensure gas-tight integrity and better torque resistance.

What sizes are available in API 5CT N80-1 casing?

API 5CT N80-1 casing is available in a wide range of standard sizes defined by the API 5CT specification:

Outside Diameter (OD): Typically ranges from 4-1/2" to 20" (114.3mm to 508.0mm).

Most Common Sizes: 5-1/2", 7", 9-5/8", and 13-3/8".

Lengths: Available in three API length ranges:

Range 1: 16 – 25 ft (4.88 – 7.62 m)

Range 2 (Standard): 25 – 34 ft (7.62 – 10.36 m)

Range 3: 34 – 48 ft (10.36 – 14.63 m)

Wall Thickness: Available in various weights (lb/ft) for each OD to meet different pressure requirements.

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